Sensors for the monitoring and/or recordation of various human physical, chemical and/or physiological parameters are known in the art. U.S. Pat. No. 4,485,813 describes a sensor that may be permanently implanted in a specific location within the human body in an implantable medical device such as a pacemaker. This sensor is used to monitor certain physical and/or physiological parameters of the subject in which it has been implanted. This sensor can be maintained in the subject for extended periods of time to continuously monitor information about the subject.
A severe limitation to the sensor described in U.S. Pat. No. 4,485,813 is the limited number of possible locations in which it can be implanted due to the requirement that the sensor be located in a medical device such as a pacemaker and the difficulty of fixation independently. This limitation on the location and fixation of the sensor limits the usefulness of the sensor for inter-lumen applications.
Sensors used to monitor parameters within lumens include sensors made of very thin membranes that are highly sensitive to mechanical pressure. As a result there is a great risk of the sensor being damaged during insertion, deployment and/or positioning. Damage to the sensor could result in poor performance or non-operability of the sensor. For example, should the membrane of a sensor break during insertion, the sensor would be rendered inoperable. Due to the risks associated with the procedures for the insertion of sensors, there would be great costs and risks involved should a sensor be damaged or destroyed during insertion. Thus, there is also a need for a device and method of protecting sensors during insertion and fixation.
For such sensors, including those machined from silicon, another concern is the erosion that the pressure-sensitive membrane undergoes when it is implanted in a patient and exposed for a prolonged period of time to bodily fluids and other naturally occurring agents inside the patient. Contrary to the prevalent view, it was discovered that a sensor machined from silicon does not exhibit a satisfactory degree of bio-compatibility with the naturally occurring bodily fluids and agents it encounters when implanted inside a patient. After a certain amount of time, these fluids and agents slowly begin dissolving the sensor, degrading the accuracy of the data produced by the sensor, and indeed, after a period of a few months, dissolving the thin membrane and other parts of the sensor completely. What is therefore needed is a bio-compatible protective coating for the sensor that resists the corrosive effect of the human body's naturally occurring fluids. By minimizing the erosion of the sensor membrane, such a protective coating would not only extend the useful life of the sensor, the coating would also maintain the accuracy of the data produced by the sensor while it is implanted inside the patient.